1. Field of the Invention
This invention relates generally to devices and methods for sizing a region of an eye or for sizing an intraocular lens placed inside an eye and, more specifically, to sizing devices and methods based, at least in part, on a test geometry of the sizing device after placement within the eye.
2. Description of the Related Art
The human eye is susceptible to numerous disorders and diseases, a number of which attack the crystalline lens. For example, cataracts mar vision through cloudy or opaque discoloration of the lens of the eye, and can result in partial or complete blindness. When this happens, the crystalline lens can be removed and replaced with an intraocular lens, or IOL. In certain other circumstances, an IOL can be placed in an eye containing the natural crystalline lens, for example, to provide for enhanced vision in the phakic eye.
A typical IOL comprises an optic body, or lens, adapted to focus light toward the retina of the eye, and one or more fixation members, or haptics, adapted to at least assist in supporting or fixating the IOL in a suitable location in the eye, such as the anterior chamber, iris, or capsular bag of the eye. The design of the fixation members is to a large part dictated by the location in the eye in which the IOL is to be implanted. In general, conditions in the anterior chamber are more exacting than in the posterior chamber, since the ocular structures in and around the anterior chamber are subject to distortion, for instance, when a patient squints, rubs, or touches his or her eyelids, engages in rigorous physical activity, or receives an unexpected jolt or impact to the body, particularly the face. As a result, it is desirable that anterior chamber IOLs be provided with relatively flexible fixation members that yield readily when ocular distortion occurs, in order to minimize irritation or trauma to the eye. At the same time, the fixation members must not yield so readily as to result in decentration of the IOL and distortion of the visual image. In addition, the fixation members preferably provide sufficient axial stability to prevent the optic from vaulting forwardly (and potentially contacting the cornea) in response to compressive forces on the outer edges of the IOL.
Sizing issue may arise when IOLs are placed inside the eye, for instance in the capsular bag, the sulcus, or the anterior chamber of the eye. For example, when an IOL is placed in the anterior chamber, the intraocular lens may be secured within the eye by fixating the distal ends of the anterior chamber IOL against the iridocorneal angle of the anterior chamber. It is important in this case to provide the proper fit between the IOL and the anterior chamber. Since the precise size of the anterior chamber is not easily determined prior to placement of an anterior chamber IOL, it may not be possible to determine how well an IOL will fit in the anterior chamber at the time it is implanted. If the anterior chamber IOL is too large (e.g., the separation between the distal ends of the unstressed haptics prior to placement in the eye are much larger than the diameter of the anterior chamber), this can lead to post-surgical complications such as endothelial cell loss, pupil ovulation, and/or pupillary block. Conversely, if the anterior chamber IOL is too small (e.g., the distal ends of the haptics do not extend far enough to engage the iridocorneal angle), the anterior chamber IOL may rotate, which can lead to endothelial cell loss, corneal decompensation, and/or other complications. Evidence of improper sizing of the anterior chamber IOLs may not occur until several weeks to as much as two years after the IOL has been implanted into the eye of a subject.
Accordingly, it would be advantageous to provide devices and methods for sizing an IOL and/or the region of the eye into which the IOL is to be placed at the time the IOL is implanted into the eye in order to reduce or avoid the aforementioned problems.